Back to EveryPatent.com
| United States Patent |
5,759,425
|
|
Miyazaki
, et al.
|
June 2, 1998
|
Honeycomb core degreasing method
Abstract
For degreasing a honeycomb core, the honeycomb core is placed in a
degreasing chamber, which is then closed. The degreasing chamber is
thereafter evacuated to a vacuum in the range of 50 to 100 torr, and the
upper and lower surfaces of the honeycomb core are sprayed with a normal
paraffin as a hydrocarbon cleaning agent heated at a temperature of from
60.degree. to 120.degree. C. for shower rinsing and finish shower rinsing.
The internal pressure of the degreasing chamber is adjusted to a vacuum in
the range of 30 to 40 torr, and a vapor of the normal paraffin cleaning
agent heated at a temperature in the range of 110.degree. to 120.degree.
C. is supplied into the degreasing chamber for vapor degreasing of the
honeycomb core. Finally, the honeycomb core is dried in the degreasing
chamber at a temperature of from 70.degree. to 120.degree. C. under a
reduced pressure in the range of 0.1 to 10 torr. The above method
degreases a honeycomb core with a satisfactory cleanliness, ensuring high
bond strength and high durability of bonds. The method is unhazardous to
environment.
| Inventors:
|
Miyazaki; Yosuke (Kakamigahara, JP);
Ogai; Koji (Kakamigahara, JP)
|
| Assignee:
|
Kawasaki Jukogyo Kabushiki Kaisha (Hyogo-Ken, JP)
|
| Appl. No.:
|
708601 |
| Filed:
|
September 5, 1996 |
Foreign Application Priority Data
| Sep 06, 1995[JP] | 7-0254602 |
| Current U.S. Class: |
216/77 |
| Intern'l Class: |
C23K 003/00 |
| Field of Search: |
216/77
|
References Cited
U.S. Patent Documents
| 3284891 | Nov., 1966 | Whitney.
| |
| 4271219 | Jun., 1981 | Brown.
| |
| 4339283 | Jul., 1982 | McCord.
| |
| 4844743 | Jul., 1989 | Koblenzer et al.
| |
| Foreign Patent Documents |
| A-5-121389 | May., 1993 | JP.
| |
| A-6-248294 | Sep., 1994 | JP.
| |
| A-7-74136 | Mar., 1995 | JP.
| |
| 470419 | Aug., 1937 | GB.
| |
| 1097297 | Jan., 1968 | GB.
| |
| 2-113-719 | Aug., 1983 | GB.
| |
Primary Examiner: Jones; Deborah
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A honeycomb core degreasing method comprising the steps of:
placing a honeycomb core in a degreasing chamber;
closing the degreasing chamber;
evacuating the degreasing chamber to a vacuum in a range of 50 to 100 torr;
spraying upper and lower surfaces of the honeycomb core with a normal
paraffin as a hydrocarbon cleaning agent heated at a temperature in a
range of 60.degree. to 120.degree. C. for shower rinsing and finish shower
rinsing;
adjusting an internal pressure of the degreasing chamber to a vacuum in a
range of 30 to 40 torr;
supplying a vapor of the normal paraffin cleaning agent heated at a
temperature in a range of 110.degree. to 120.degree. C. into the
degreasing chamber for a vapor degreasing of the honeycomb core; and
drying the honeycomb core in the degreasing chamber at a temperature in a
range of 70.degree. to 120.degree. C. under a reduced pressure in a range
of 0.1 to 10 torr.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a honeycomb core degreasing method for
degreasing a honeycomb core for a honeycomb sandwich structural material
before being sandwiched between outer sheets.
2. Description of the Related Art
A basic honeycomb sandwich structural material is constructed by laminating
and bonding a honeycomb core, i.e., a core member, between two outer
sheets. A honeycomb sandwich structural material for aircraft and space
craft has outer sheets and a metallic honeycomb core. The outer sheets are
made of a metal, such as an aluminum alloy or a titanium alloy, a
synthetic resin, such as a GFRP, CFRP, AFRP OR BFRP, or a composite resin
material, such as a fiber-reinforced composite material. The metallic
honeycomb core is made of aluminum alloy or a nonmetallic honeycomb core
of glass, aramid fibers or the like.
The outer sheets are bonded to the honeycomb core with an adhesive film of
a thermosetting epoxy resin that sets at 250.degree. C. or 350.degree. C.
The outer sheets and the honeycomb core must be cleaned by a cleaning
process before a bonding process to ensure the firm adhesion of the outer
sheets and the honeycomb core and satisfactory durability of bonds because
the adhesion of the outer sheets and the honeycomb core is primary or
secondary structural adhesion and the strength and the durability of
structures are greatly dependent on the adhesive performance and the
durability of bonds.
A pretreatment process for adhesive bonding the outer sheets uses vapor
degreasing, etching, anodizing or blasting, and, when necessary, an
adhesive primer is applied to the surfaces of the outer sheets and bake
cured. A pretreatment process for adhesive bonding the honeycomb core uses
solvent cleaning when the honeycomb core is made of a nonmetallic material
or vapor degreasing when the honeycomb core is made of a metal. When
assembling the honeycomb core and the outer sheets by adhesive bonding,
the outer sheets are bonded to the honeycomb core with an adhesive film,
to construct a honeycomb sandwich structure, and then the honeycomb
sandwich structure is pressured and heated to harden the adhesive film.
Incidentally, most metal honeycomb cores are aluminum alloy honeycomb
cores. An aluminum alloy honeycomb core is formed by partially bonding
together aluminum alloy foils in a laminated structure and expanding the
laminated structure to form a honeycomb core. The honeycomb core thus
formed by expanding the laminated structure has bonds, which is called
node bonds, and, in most cases, the honeycomb core is of a hexagonal cell
type having hexagonal cells. Some honeycomb cores are of a square cell
type, an overexpanded type or an open cell type, i.e., a core formed by
stacking and bonding together corrugated ribbons.
A conventional pretreatment process for cleaning an aluminum alloy
honeycomb core before a bonding process carries out open-space degreasing
using a chlorinated solvent, such as trichloroethane, or closed-space
vapor degreasing. The use and production of trichloroethane has been
prohibited by law since the end of 1995 for the conservation of the
ozonosphere because trichloroethane is a substance that destroys the
ozonosphere.
Prior art techniques relating to the field to which the present invention
is related are disclosed in JP-A Nos. 5-121389, 6-248294 and 7-74136.
When an aluminum alloy honeycomb core is degreased by using an aqueous
degreasing agent, water and the degreasing agent are liable to remain on
the edge or faying recess of the aluminum alloy honeycomb core due to the
surface tension of water and the degreasing agent, so that the degreasing
agent attacks and harms the honeycomb core. Therefore, it is inappropriate
to use an aqueous degreasing agent as a substitute for trichloroethane and
such an aqueous degreasing agent has not been used for degreasing.
Currently, returning back to an old process, only a vapor degreasing
process employing trichloroethylene or tetrachloroethylene is used for
degreasing the aluminum alloy honeycomb core. However, the vapor
degreasing process using trichloroethylene is hazardous to operator's
health and has the possibility of entailing soil contamination, and hence
many legal restrictions are imposed on the vapor degreasing process.
The performance of the pretreatment process for cleaning the aluminum alloy
honeycomb core before a bonding process affects the performance of a
honeycomb sandwich panel in the following respects.
(1) The application of an adhesive primer to the surface of the aluminum
alloy honeycomb core.
(2) The adhesion of the aluminum alloy honeycomb core and outer sheets
(formation of fillets of the adhesive).
(3) The adhesion of spliced aluminum alloy honeycomb cores (adhesion of the
butt joint of aluminum alloy honeycomb cores).
(4) Filling aluminum alloy honeycomb cores with a resin.
If aluminum alloy honeycomb cores are not cleaned and contaminated, a
honeycomb sandwich structure constructed by sandwiching the aluminum alloy
honeycomb core between outer sheets does not have a necessary strength,
and the outer skins of the honeycomb sandwich structure may be separated
from each other. Accordingly, it is important to improve the performance
of the pretreatment process for cleaning aluminum alloy honeycomb cores.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a honeycomb core
degreasing method for degreasing a honeycomb core before a bonding
process, which is capable of degreasing an aluminum alloy honeycomb core
with a satisfactory cleanliness to ensure high bond strength and high
durability of bonds, and which is unhazardous to the operators and the
environment.
The inventors of the present invention made studies of aqueous decreasing
methods using an aqueous degreasing agent and solvent degreasing methods
using an organic solvent.
An aqueous degreasing method uses an aqueous solution containing an
alkaline salt or a surface active agent as a principal component, immerses
a workpiece in the aqueous solution or sprays a workpiece with the aqueous
solution, the aqueous solution being of a temperature not lower than the
cloud point. The aqueous degreasing method was found to be unsuitable for
degreasing aluminum alloy honeycomb cores. When an aluminum alloy
honeycomb core is degreased by an aqueous degreasing method, the strength
of bonds (node bonds) adhesively bonding together aluminum foils was
reduced due to the moisture absorption of the adhesive, and aluminum alloy
honeycomb cores cleaned by the aqueous degreasing method were corroded
during manufacture or during use by residual alkaline salts and moisture
remaining in the aluminum alloy honeycomb cores.
Aluminum alloy honeycomb cores were cleaned by solvent degreasing methods
respectively using hydrocarbon solvents, such as NMP, a normal paraffin,
an isoparaffin and a napthene, water base solutions, such as aqueous
solutions containing an alcohol as a principal component, water and a
surface active agent, halides, alcohols and ketones, and the effects of
the solvent degreasing methods were evaluated on the basis of criteria
tabulated in Table 1 below. The results of evaluation are tabulated in
Table 2 below. It was found through the examination of the results of
evaluation shown in Table 2 that a normal paraffin cleaning agent (NS
CLEAN 200, trade name of a cleaning agent produced by NIKKO PETROCHEMICALS
CO., LTD., Japan) is practically applicable to degreasing aluminum alloy
honeycomb cores before a bonding process.
TABLE 1
__________________________________________________________________________
Test Quality
Test Item
Test Method (Note 3) Criteria
Remarks
__________________________________________________________________________
1 Degreasing
Cleanliness
Contaminate a sample core degreased by vapor
degreasing Equivalent to
Note 1)
Performance with oil, clean the contaminated sample core by
immersion trichloroethan
Contaminating Oil:
cleaning, dry the cleaned sample core, and measure
Lubrication oil for
quality of residual oil. (Note 1) honeycomb core
Dryness Measure residual degreasing agent by FT-IR. Dry the
sample Not to detect
fabrication machine
at 130.degree. C. for 30 min. Use an evaporated gold
surface as a molecular bond
Note 2)
reference surface. degreasing agent
Adhesive: AF163-2K
2 Effect on
Effect on Surface
Immerse the sample core in a degreasing agent for 3 hr.
and Equivalent to
Adhesive Primer:
Workpiece
Coating heat the sample core at 170.degree. C. for 3 hr.
Subject the sample trichloroethan
EC3960
to a salt water spray test (ASTM B117) for 720 hr.
Observe corrosion and
Cure:
the appearance of the sample core and measure weight
loss weight loss
As specified by
maker
(MIL-C-7438G, Core corrosion test).
Note 3)
Effect on Node
Immerse a sample core degreased by vapor degreasing in
a Equivalent to
Sample honeycomb
core
Bond Strength
degreasing agent for 3 hr., dry at 100.degree. C. for
30 min. and trichloroethan
5.7-3/16-20N(5056)
subject the sample core to strength test
MIL-C-74388G,
Delamination test). The blank is not subjected to
heating, HEXCEL CR III
such as drying.
3 Bond Quality
Honeycomb Panel
Degrease a sample core as procured by immersing the
same in Equivalent to
Drum Peel
the degreasing agent for 3 min. or by spray degreasing,
dry trichloroethan
Strength Test
the degreased sample core at 100.degree. C. for 30
min., construct a
honeycomb sandwich panel using the sample core. Subject
the
honeycomb sandwich panel to strength test (ASTM D1781).
(Note 2)
Bond Durability
Clean and dry the degreased sample aluminum plate, bond
the Equivalent to
Test sample aluminum plate, subject the bonded sample
aluminum trichloroethan
plate to wedge test (ASTM D3726).
4 Chemical
Chemical Analysis
Chemical analysis (MIL-T-81533)
pH: 5.0-10.5
Property
of Halides Not less than 0.06
wt %
__________________________________________________________________________
TABLE 2
__________________________________________________________________________
Effect on
Effect on the
Drum Peel
Bond Overall
Degreasing
Cleanli- the Surface
Strength of
Strength
Durability
Judge-
agent ness
Dryness
Coating
Node Bond
Test Test ment
Remarks
__________________________________________________________________________
1 N-methyl-2-
.largecircle.
Not measured
-- X .largecircle.
-- X Note 1)
pyrolidone .largecircle.: Equivalent
to 1.1.1-trichloroethan
2 Normal .largecircle.
Not measured
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
X: Inferior to
1.1.1-trichloroethan
paraffin Note 2)
3 Isoparaffin
.largecircle.
Not measured
X X X -- X Result of chemical
analysis of halide
4 Naphthene
.largecircle.
Not measured
X .largecircle.
.largecircle.
-- X degreasing agent
5 Quasi-aqueous
X Not Measured
X .largecircle.
X -- X (only for bromide)
hydrocarbon Not satisfy the criteria
for pH
6 Bromide
.largecircle.
Not measured
-- -- -- -- X
hydrocarbon Note 2)
7 Isopropyl
X Not measured
-- .largecircle.
.largecircle.
.largecircle.
alcohol
8 Methyl-ethyl
.largecircle.
Not measured
-- X .largecircle.
.largecircle.
ketone
9 1.1.1- .largecircle.
Not measured
.largecircle.
.largecircle.
.largecircle.
.largecircle.
--
trichloroethane
10 Blank (not
-- Not measured
-- .largecircle.
-- -- --
degreased)
__________________________________________________________________________
The present invention has been made on the basis of such findings obtained
through the examination of those results of evaluation and provides a
honeycomb core degreasing method employing a vacuum spraying vapor
cleaning process using a normal paraffin as a hydrocarbon cleaning agent,
and capable of degreasing honeycomb cores more satisfactorily than the
conventional honeycomb core degreasing method employing a vapor degreasing
process using trichloroethane or trichloroethylene.
According to the present invention, a honeycomb core degreasing method
comprises the steps of placing a honeycomb core in a degreasing chamber,
closing the degreasing chamber, evacuating the degreasing chamber to a
vacuum in a range of 50 to 100 torr, spraying upper and lower surfaces of
the honeycomb core with a normal paraffin as a hydrocarbon cleaning agent
heated at a temperature in a range of 60.degree. to 120.degree. C. for
shower rinsing and finish shower rinsing, adjusting an internal pressure
of the degreasing chamber to a vacuum in a range of 30 to 40 torr,
supplying a vapor of the normal paraffin cleaning agent heated at a
temperature in a range of 110.degree. to 120.degree. C. into the
degreasing chamber for a vapor degreasing of the honeycomb core, and
drying the honeycomb core in the degreasing chamber at a temperature in a
range of 70.degree. to 120.degree. C. under a reduced pressure in a range
of 0.1 to 10 torr.
The honeycomb core degreasing method of the present invention evacuates the
degreasing chamber to a vacuum in the range of 50 to 100 torr to avoid the
temperature to rise near to the boiling point of the normal paraffin
cleaning agent when temperature distribution in the degreasing chamber is
irregular and to promote the penetration of the normal paraffin cleaning
agent into gaps in the honeycomb core.
The higher the pressure of the degreasing chamber or the lower the
temperature of the degreasing chamber, the longer is the time necessary
for drying the honeycomb core. Therefore, the drying step, i.e., the final
process is carried out at a vacuum in the range of 0.1 to 10 torr and a
temperature in the range of 70.degree. to 120.degree. C. The allowable
pressure range and the allowable temperature range were determined on the
basis of a drying time practically allocatable to the drying step. The
upper limit of the allowable temperature range was set to 120.degree. C.
taking into consideration the resistance to heat of the node bonds and so
on of honeycomb cores.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a honeycomb core degreasing apparatus for
carrying out a honeycomb core degreasing method in accordance with the
present invention;
FIG. 2 is a perspective view of an aluminum alloy honeycomb core having
hexagonal cells to be degreased by the honeycomb core degreasing apparatus
of FIG. 1;
FIG. 3 is a perspective view of a basket for containing a honeycomb core
during degreasing;
FIG. 4 is a partly broken perspective view of a honeycomb sandwich panel
constructed by adhesively bonding aluminum alloy outer sheets to the
opposite major surfaces of a degreased aluminum alloy honeycomb core
having hexagonal cells; and
FIG. 5 is a graph showing variations of the vapor pressures of normal
paraffins with temperature.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be understood from the
following detailed description made with reference to the accompanying
drawings.
The method of degreasing a honeycomb core according to the present
invention uses a normal paraffin as a hydrocarbon cleaning agent that is
sprayed in a closed degreasing chamber in which the honeycomb core is
placed. Steps of the degreasing method are all carried out in the closed
degreasing chamber and hence there is no danger of fire. Since the flash
point of the normal paraffin cleaning agent is 70.degree. C., there is a
high possibility of fire when the normal paraffin cleaning agent is
sprayed for shower cleaning and the degreased honeycomb core is dried in
an open space because a mist of the normal paraffin cleaning agent is
liable to form under such conditions. There is no possibility of fire when
the honeycomb core is subjected to shower cleaning and drying in the
closed degreasing chamber.
The honeycomb core degreasing method of the present invention subjects the
two major surfaces of a honeycomb core to a shower rinsing process and a
finish rinsing process using the normal paraffin cleaning agent of a
temperature in the range of 60.degree. to 120.degree. C. in the degreasing
chamber evacuated to a vacuum in the range of 50 to 100 torr, whereby
inner surfaces of the honeycomb core can perfectly be degreased. Since the
honeycomb core constructed by partially bonding together foils has a small
heat capacity, mineral oils contaminating a honeycomb core cannot
completely be removed to a degree at which no residual mineral oil can be
detected by ultraviolet inspection using ultraviolet radiation for
detecting residual oils by a single vapor degreasing cycle of the
conventional honeycomb core degreasing method using trichloroethylene. The
honeycomb core degreasing method of the present invention uses the normal
paraffin as a hydrocarbon cleaning agent of a temperature in the range of
60.degree. to 120.degree. C., at which the normal paraffin cleaning agent
is able to remove (dissolve) mineral oils contaminating the honeycomb core
efficiently, and evacuates the degreasing chamber to a vacuum of 50 to 100
torr, at which the normal paraffin cleaning agent can be supplied at an
appropriate rate into the degreasing chamber. Consequently, the inner
portions of the honeycomb core can completely be degreased. The honeycomb
core degreasing method of the present invention is effectively applicable
to degreasing a honeycomb core with an outer sheet adhesively attached to
one major surface thereof.
The honeycomb core degreasing method of the present invention adjusts the
internal pressure of the degreasing chamber to a vacuum in the range of 30
to 40 torr after a shower rinsing process and a finish shower rinsing
process have been completed, and then supplies a vapor of the normal
paraffin cleaning agent of a temperature in the range of 110.degree. to
120.degree. C. into the degreasing chamber for vapor degreasing. Such
degreasing steps are effective in enhancing the effect of finish cleaning
and promoting drying. The normal paraffin cleaning agent has a boiling
point and a flash point very close to the boiling point at the normal
pressure and hence the normal paraffin cleaning agent cannot be used for
vapor degreasing at the normal pressure. However, the normal paraffin
cleaning agent can be used for vapor degreasing at a reduced pressure
because the boiling point of the normal paraffin cleaning agent decreases
when the pressure is reduced. When the cleaning temperature is set to
120.degree. C., which is equal to a temperature at which the honeycomb
core and outer sheets are heated when bonding the outer sheets to the
honeycomb core, in view of the resistance to heat of the honeycomb core,
the vapor degreasing of the honeycomb core for finish cleaning can
properly be accomplished without leaving any residual oils when the
degreasing chamber is evacuated to a vacuum in the range of 30 to 40 torr,
which is understood from FIG. 5, and the subsequent drying can be
promoted.
The honeycomb core degreasing method of the present invention carries out
the drying process, i.e., the final process, at a reduced pressure in the
range of 0.1 to 10 torr and at a temperature in the range of 70.degree. to
120.degree. C., the normal paraffin cleaning agent remaining on the
honeycomb core can completely be removed and satisfactory drying can be
achieved.
Thus, the honeycomb core degreasing method of the present invention
degreases a honeycomb core with a satisfactory cleanliness, and ensures
sufficient bond strength, durability of bonds and safety for the operator
and the environment.
A honeycomb core degreasing apparatus for carrying out the honeycomb core
degreasing method of the present invention will be described prior to the
description of the honeycomb core degreasing method.
Referring to FIG. 1, a degreasing vessel 1 defining a degreasing chamber
has a door 2 on its left end, as viewed in FIG. 1, upper shower nozzles 3
for spraying a normal paraffin degreasing agent on the upper surface of a
honeycomb core are disposed in an upper portion of the degreasing chamber,
and lower shower nozzles 4 for spraying the degreasing agent on the lower
surface of the honeycomb core are disposed in a lower portion of the
degreasing chamber. A holder 5 for holding the honeycomb core is disposed
in the central portion of the degreasing chamber. The upper shower nozzles
3 and the lower shower nozzles 4 are full-cone nozzles disposed with their
axes in parallel to the direction of the width of a honeycomb core held on
the holder 5. The shower nozzles 3 and 4 are arranged so that a cleaning
area of 3700 mm by 1700 mm is substantially uniformly sprayed with the
degreasing agent in substantially the same flow density. A heat exchanger
6a for heating the degreasing chamber is provided in the lower righthand
portion of the degreasing chamber.
The upper shower nozzles 3 and the lower shower nozzles 4 are connected via
a degreasing agent supply line 8 to a reservoir tank 7 containing the
degreasing agent and to a return tank 16. A heat exchanger 6b is disposed
in the reservoir tank 7 to regulate the temperature of the degreasing
agent. A vacuum pump 9 is connected to the degreasing vessel 1 by a
suction line 10 to evacuate the degreasing chamber. A condenser 11 is
placed in the suction line 10. An evaporator 12 is connected to the
degreasing vessel 1 via a vapor supply line 13 to supply the vapor of the
degreasing agent into the degreasing chamber. A heat exchanger 6c is
placed within the evaporator 12 and connected to an oil heater 14. A drain
tank 15 is connected to the evaporator 12. The degreasing agent supplied
into and used in the degreasing chamber of the degreasing vessel 1 is
returned to a return tank 16. The return tank 16 is connected to the
evaporator 12 via a regeneration line 17 and to the degreasing agent
supply line 8 via a return line 18. Another heat exchanger 6d is placed in
the return tank 16 to regulate the temperature of the degreasing agent
contained in the return tank 16.
A heating oil heated by the oil heater 14 is supplied to the heat
exchangers 6a, 6b and 6d placed in the degreasing vessel 1, the reservoir
tank 7 and the return tank 16, respectively, to regulate the respective
temperatures of the degreasing vessel 1, the reservoir tank 7 and the
return tank 16. The degreasing agent condensed by the condenser 11 is
returned through a return line 19 to the reservoir tank 7.
If necessary, an exhaust hood 20 may be disposed above the door 2 of the
degreasing vessel 1 to enable the use of trichloroethylene for degreasing.
The vented hood 20 is connected via a duct 21 to an exhaust device 22.
An example of the honeycomb core degreasing method according to the present
invention to be carried out by the thus constructed honeycomb core
degreasing apparatus will be described below. A hexagonal cell type
aluminum alloy honeycomb core 25 of 3500 mm in length, 1600 mm in width,
100 mm in thickness and 6 mm in cell size as shown in FIG. 2 was placed in
a stainless steel basket 26 of 3700 mm in length, 1700 mm in width and 150
mm in depth as shown in FIG. 3. The door 2 was opened, the basket 26
containing the aluminum alloy honeycomb core 25 was carried into the
degreasing chamber in the degreasing vessel 1 by a truck, and the basket
26 was held on the holder 5 disposed in the central portion of the
degreasing chamber. Gases discharged from the degreasing vessel 1 were
discharged through the exhaust hood 20 and the duct 21 by the exhaust
device 22. Subsequently, the door 2 was closed, the degreasing chamber 1
was evacuated through the suction line 10 by the vacuum pump 9 to a vacuum
of 100 torr. Then, the degreasing chamber was heated at 70.degree. C. by
the heat exchanger 6a. A normal paraffin degreasing agent 27 containing a
hydrocarbon having a carbon number of 11 or 12 as a principal component
(for example, NS CLEAN 200, trade name of a degreasing agent produced by
NIKKO PETROCHEMICALS CO., LTD., Japan) is supplied from the return tank 16
through the supply lines 18 and 8 to the upper shower nozzle 3 and the
lower shower nozzles 4, and the normal paraffin degreasing agent 27 was
sprayed on the upper and the lower surfaces of the honeycomb core 25 for 7
minutes for shower rinsing. Subsequently, a fresh degreasing agent was
supplied from the reservoir tank 7 through the supply line 8 to the upper
shower nozzles 3 and the lower shower nozzles 4 and sprayed on the upper
and lower surface of the honeycomb core 25 for 20 seconds for finish
shower rinsing. Then, the degreasing chamber was evacuated to 40 torr, the
normal paraffin degreasing agent 27 was heated at 120.degree. C. in the
evaporator 12 by the oil heater 14 to produce a vapor of the normal
paraffin degreasing agent 27, and the vapor of the normal paraffin
degreasing agent 27 of 120.degree. C. was supplied through the vapor
supply line 13 into the degreasing chamber to remove oils remaining on the
honeycomb core 25 completely. Subsequently, the pressure in the degreasing
chamber was adjusted to 1 torr, and then the honeycomb core 25 was dried
at 100.degree. C. for 4 minutes.
The used normal paraffin degreasing agent 27 collected on the bottom of the
degreasing vessel 1 was returned to the return tank 16 and filtered in the
return tank 16. Part of the filtered normal paraffin degreasing agent 27
was sent through the line 17 to the evaporator 12 and the rest of the
filtered normal paraffin degreasing agent 27 was supplied through the
return line 18 to the supply line 8 to use the same agin for shower
rinsing. The vapor of the normal paraffin degreasing agent contained in
the gas sucked by the vacuum pump 9 to regulate the vacuum of the
degreasing chamber was condensed by the condenser 11, and the condensed
normal paraffin degreasing agent 27 was returned to the reservoir tank 7.
The thus degreased and cleaned honeycomb core 25 was completely removed of
contaminating mineral oils, and the vapor degreasing ensured the complete
removal of the residual mineral oils from the honeycomb core 25. No
residual mineral oil could be detected by ultraviolet inspection using
ultraviolet radiation for detecting residual oils. The honeycomb core 25
could be dried satisfactorily and the normal paraffin degreasing agent was
completely removed by drying at the reduced pressure at 100.degree. C. for
4 minutes.
Thermosetting epoxy adhesive films having a setting temperature of
250.degree. F. were applied to the upper and the lower surface of the thus
cleaned honeycomb core 27, and, as shown in FIG. 4, aluminum alloy outer
sheets 28 were attached adhesively to the upper and the lower surface of
the honeycomb core 25. Thereafter the assembly of the honeycomb core 25,
the thermosetting adhesive films and the aluminum alloy outer sheets 28
was compressed and heated to complete a honeycomb sandwich panel 29. The
honeycomb sandwich panel had a sufficiently high bond strength, sufficient
durability of bonds and a high structural strength.
The honeycomb core degreasing method of the present invention is applicable
also to degreasing various types of honeycomb cores including stainless
steel honeycomb cores, titanium honeycomb cores, square cell type
honeycomb cores, open cell type honeycomb cores and overexpanded type
honeycomb cores.
The honeycomb core 25 may be of any cell size, provided that the degreasing
agent sprayed by the upper shower nozzles 3 and the lower shower nozzles 4
is able to penetrate into the cells. Although full cone type nozzles are
suitable for use as the upper shower nozzles 3 and the lower shower
nozzles 4, the upper shower nozzles 3 and the lower shower nozzles 4 may
be those that sprays the degreasing agent at a not very high spraying
pressure as long as the liquid degreasing agent is able to wet the
honeycomb core 25 thoroughly.
As is apparent from the foregoing description, the honeycomb core
degreasing method of the present invention using a normal paraffin as a
hydrocarbon degreasing agent and employing a vacuum spraying process and a
vapor degreasing process is capable of perfectly degreasing honeycomb
cores with a satisfactory cleanliness. Accordingly, a honeycomb sandwich
panel constructed by adhesively bonding outer sheets to a honeycomb core
degreased by the honeycomb core degreasing method of the present invention
has sufficient bond strength, durability of bonds and a high structural
strength.
Since the honeycomb core degreasing method of the present invention is
carried out in a closed degreasing chamber, safety can be secured for the
operator and the environment.
Top